EXHIBIT 99.255
[ISO ALLIANCE LETTERHEAD]
September 18, 1997
Mr. Steve Callahan
Coopers & Lybrand L.L.P.
5000 Executive Parkway, Suite 300
San Ramon, CA 94583
Re: Redistribution of SA Functionality
Dear Mr. Callahan:
Pursuant to several email notes and the discussion at the September 11 meeting
of the ISO Executive Steering Committee, this letter provides official
notification of the redistribution of some SA functionality. Specifically, the
Outage Scheduler (OS) and Similar Day Load Forecast (LF) modules have been
moved from the SA environment to the SI environment, primarily to avoid an
Oracle licensing issue which would have adversely affected the production
environment.
The functionality of the Interchange Scheduling Calculation (ISC) module has
been redistributed within the SA Subsystem; i.e., there no longer exists an ISC
module per se. Details of this are outlined in the enclosure.
These changes will be transparent to the user.
These changes will be captured in our testing plans and training materials.
Please indicate your receipt of this document by returning a signed copy of the
enclosed receipt. For your convenience, we have included a self-addressed
stamped envelope.
Yours truly,
/s/ S.R. INGRAM
S.R. Ingram
Enclosures
cc: Skadden, Arps, Slate, Meagher & Flom, LLP
ATTN: M.R. Hoffmann
Perot Systems
ATTN: Chuck Bell
ABB Systems Control
ATTN: Philip Curtis
Ernst & Young, LLP
ATTN: Bill Hunter
INTERCHANGE SCHEDULING CALCULATION (ISC) FUNCTIONALITY
The following describes the spreading of the ISC functionality among other
functions in the SA/SI subsystems. For ease of review, text from the DSOW is
provided, followed by amplifying statements from the design team, which are
underlined for clarity.
VOLUME 3, SECTION 1.3, OVERVIEW OF DAY-AHEAD SCHEDULING PROTOCOLS AND TIMING
3) By 0600 of the day preceding the next operating day, each SC will provide to
the ISO a forecast of hourly loads for which it will schedule generation
resource deliveries for the next seven operating days, including the
location. The ISO will aggregate all the non-PX loads by Utility
Distribution Company (UDC)-specific location and will provide by 0630 these
aggregate loads to each UDC.
The above referenced aggregation is performed within the SI subsystems.
8) At 1100, the SCs submitted next day's Preferred Schedules will be frozen.
The ISO will validate all SC Preferred Schedules, self-provided ancillary
service schedules and bids and will then notify and resolve incorrect
schedules and bids, if any. Also, as part of the validation process, the ISO
will ensure Preferred Schedules are balanced.
9) During this time, the ISO will additionally start the inter-zonal congestion
management evaluation process and ancillary service requirement assessment
and bid evaluation.
10) If there is no inter-zonal congestion, the ISO will move onto #15. If
inter-zonal congestion exists, by 1200 the ISO will determine and notify
each SC of their Advisory Re-dispatch Schedules and the transmission prices
of the congested interfaces.
11) Also at 1200, the ISO will notify the SCs of the advisory ancillary service
schedules and associated prices (results of bid evaluation and self-provided
schedule information).
12) By 1300 SCs may adjust their Preferred Schedules in response to the ISO's
Advisory Re-dispatch schedules and transmission prices for the use of
congested interfaces, and may submit Revised Preferred Schedules to the ISO.
SCs may also submit revised self-provided ancillary service schedules and/or
ancillary service bids.
13) After receiving, ISO will validate the Revised Preferred Schedules, revised
self-provided ancillary service schedules and revised ancillary service
bids, notify and resolve incorrect schedules and bids, if any.
14) Additionally, ISO will re-run its inter-zonal congestion management
evaluation process and its ancillary service requirement and bid evaluation
process using the Revised Preferred Schedules and revised self-provided
ancillary services and ancillary service bids.
15) Once the above final inter-zonal congestion management and ancillary service
assessment and bid evaluation is complete, the ISO will then begin the
intra-zonal congestion management process.
16) ...
17) Also by 1400, the ISO will develop the net schedules for each of the control
area interfaces. ISO then verifies with the adjacent control areas that
their net schedules at these interfaces match, will search for and resolve
discrepancies. Once agreed, the ISO's day-ahead schedule coordination
responsibilities are completed. The final Committed Schedules will be
transferred into the BBS. The Committed Schedules will also be converted
into Operating Schedules which, together with other generation control
information, will be transferred into ISO Power Management System (PMS).
Item 17 is the ISC functionality and is merged into items 9-15 that are
performed by ???? and ASM functions.
Control Number: 177
VOLUME 3, SECTION 10.3, INTERCHANGE SCHEDULING CALCULATION (ISC)
The Interchange Scheduling Calculation function will calculate net area
interchanges based on the final Committed Schedules after transmission
assessment applications determine any re-dispatch due to congestion or
other reliability requirements. The net area interchange values will be
sent to the PMS to its Interchange Transaction Scheduler (ITS) and for use
in real time operation functions.
Once the Preferred Schedules are received from the Scheduling
Infrastructure, the schedules must be grouped and mapped to reflect the
physical characteristics of the transmission system and serve as the "input
file" to the Transmission Assessment and Congestion Management
applications. The ISC functions will compute ISO greater control area net
interchange, area net interchange schedules for the former control areas of
the ACCs, and zonal net interchange schedules before assessing the
feasibility of the Preferred Schedules vis-a-vis the transmission system.
This application (ISC) is also required to group (through computation) the
final day-ahead or hour-ahead committed schedules in a format compatible
with the ISO control area and ACCs before sending them to the ISO ITS and
dispatch PMS. This (ISC) application function consists of the following
computations:
1) Compute ISO net hourly interchange schedules for:
- Control Area Intertie Points;
- Control Area Net Interchange;
- Net interchange between the ACCs based on a pre-specified geographic
boundaries;
- Inter-Zonal Net Interchange; and
- Zonal and intertie grouping and sorting of (1) load, (2)
generation, (3) Ancillary Services, and (4) interchanges (intertie
and zonal) schedules.
2) Perform automatic validation of the ISO net interchange schedules
calculated in step (1) above to ensure that the final accepted
schedules are within the limits of the transmission line(s)' (path)
capacity which is specified by the ISO and is calculated using the
Transmission Assessments Applications both at the intertie points and
across inter-zonal paths.
The above ISC requirements are considered in CONG and ASM subsystems. Since
both CONG and ASM have both day ahead and hour ahead modes, the ISC
functionality will have both day ahead and hour ahead modes also.
[ISO ALLIANCE LOGO] 1000 South Fremont
Suite A-11
Alhambra, CA 91803
CONFIRMATION OF RECEIPT
September______, 1997
I am in receipt of your document with control number 177, Redistribution of SA
Functionality.
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